Retarded Cement Compositions and Methods for Well Completions

ABSTRACT

Cement retarders are based on blends of lignosulfonate compounds, borate compounds and gluconate compounds. The compounds are present in certain ratios that allow the retarders to operate at temperatures and pressures up to and exceeding about 176° C. and 152 MPa. The retarders may also be provided in liquid form, improving their suitability for use at offshore well-site locations.

BACKGROUND

The statements in this section merely provide background informationrelated to the present, disclosure and may not constitute prior art.

This disclosure relates to compositions and methods for treatingsubterranean formations, in particular, compositions and methods forcementing subterranean wells.

During the construction of subterranean wells, it is common, during andafter drilling, to place a tubular body in the wellbore. The tubularbody may comprise drillpipe, casing, liner, coiled tubing orcombinations thereof. The purpose of the tubular body is to act as aconduit through which desirable fluids from the well may travel and becollected. The tubular body is normally secured in the well by a cementsheath. The cement sheath provides mechanical support and hydraulicisolation between the zones or layers that the well penetrates. Thelatter function is important because it prevents hydraulic communicationbetween zones that may result in contamination. For example, the cementsheath blocks fluids from oil or gas zones from entering the water tableand polluting drinking water. In addition, to optimize a well'sproduction efficiency, it may be desirable to isolate, for example, agas-producing zone from an oil-producing zone. The cement sheathachieves hydraulic isolation because of its low permeability. Inaddition, intimate bonding between the cement sheath and both thetubular body and borehole is necessary to prevent leaks.

Optimal cement-sheath placement often requires that the cement slurrycontain a retarder. Cement retarders delay the setting of the cementslurry for a period sufficient to allow slurry mixing and slurryplacement in the annular region between the casing and the boreholewall, or between the casing and another casing string.

A wide range of chemical compounds may be employed as cement retarders.The most common classes include lignosulfonates, cellulose derivatives,hydroxycarboxylic acids, saccharide compounds, organophosphonates andcertain inorganic compounds such as sodium chloride (in highconcentrations) and zinc oxide. A more complete discussion of retardersfor well cements may be found in the following publication—Nelson E B,Michaux M and Drochon B: “Cement Additives and Mechanisms of Action,” inNelson E B and Guillot D. (eds.): Well Cementing (2^(nd) Edition),Schlumberger, Houston (2006) 49-91.

Certain types of retarders have been blended with other compounds toextend their useful temperature range, improve cement-slurry properties,or both. For example, the useful temperature range of certainlignosulfonate retarders may be extended to more than 260° C. by addingsodium tetraborate decahydrate (borax). Sodium gluconate may be blendedwith a lignosulfonate and tartaric acid to improve the rheologicalproperties of the cement slurry. Thus, a myriad of retarders andretarder blends exist which may be applicable to a wide range ofsubterranean-well conditions.

Cement-retarder technology for well cements is sophisticated; however,as exploration and production operations continue to move intoenvironmentally sensitive areas, the population of retarders that may beused is increasingly restricted. This is particularly true in the NorthSea. The countries that operate in the North Sea (UK, Norway, Denmarkand Holland) maintain a list of chemical products that “pose little orno risk to the environment”. These materials should meet the followingcriteria. (1) All of the organic components present in the material mustbe biodegradable in seawater. (2) All of the components should have alow toxicity to fish (Scophthalamus Maximum), marine species (AcartiaTonsa) and algae (Skeletonema Costatum). (3) All of the componentsshould not bioaccumulate. (4) The additive should not contain anyprohibited chemicals.

It thus becomes more and more challenging to develop efficient cementretarders (and other types of additives) that can meet these criteria.This is especially true when the cement slurries must be placed inhigh-pressure/high-temperature (HPHT) wells.

Despite the valuable contributions of the prior art, it would beadvantageous to have efficient retarders which perform suitably in HPHTenvironments. In addition, for logistical reasons in offshore locations,it would be advantageous if the retarders were available in liquid form.

SUMMARY

In an aspect, embodiments relate to well-cementing compositions. In afurther aspect, embodiments relate to methods for cementing asubterranean well. In yet a further aspect, embodiment relate to uses ofPortland-cement retarders comprising a borate compound, a lignosulfonatecompound and a gluconate compound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the effect of the sodiumlignosulfonate-to-sodium gluconate ratio on the thickening time ofcement slurries containing sodium tetraborate decahydrate.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation—specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein can also comprise some components other than thosecited. In the summary and this detailed description, each numericalvalue should be read once as modified by the term “about” (unlessalready expressly so modified), and then read again as not so modifiedunless otherwise indicated in context. Also, in the summary and thisdetailed description, it should be understood that a concentration rangelisted or described as being useful, suitable, or the like, is intendedthat any and every concentration within the range, including the endpoints, is to be considered as having been stated. For example, “a rangeof from 1 to 10” is to be read as indicating each and every possiblenumber along the continuum between about 1 and about 10. Thus, even ifspecific data points within the range, or even no data points within therange, are explicitly identified or refer to only a few specific, it isto be understood that inventors appreciate and understand that any andall data points within the range are to be considered to have beenspecified, and that inventors possessed knowledge of the entire rangeand all points within the range.

All ratio or percentages described here after are by weight unlessotherwise stated.

As stated earlier, it would be advantageous to have cement retardersthat meet the “North-sea” list criteria and operate efficiently in aHPHT environment—preferably at temperatures as high as at least 176° C.(350° F.) and 152 MPa (22,000 psi). In addition, availability of theretarder in liquid form would be desirable. The inventors have providedsuch retarders. They discovered that certain blends of lignosulfonates,gluconates and borates satisfy the goals described above.

Embodiments relate to well-cementing compositions that comprise Portlandcement, water and a retarder comprising a lignosulfonate compound, aborate compound and a gluconate compound. The retarder is formulatedsuch that the lignosulfonate:borate-compound concentration ratio isbelow about 0.75:1. The composition may also be pumpable. Those skilledin the art will recognize that a pumpable cement slurry usually has aviscosity lower than 1000 mPa-s at a shear rate of 100 s⁻¹.

The lignosulfonate compound may be (but would not be limited to) sodiumlignosulfonate, calcium lignosulfonate, ammonium lignosulfonate andcombinations thereof. The gluconate compound may be (but would not belimited to) sodium gluconate, calcium gluconate, ammonium gluconate,zinc gluconate, iron gluconate and combinations thereof. Sodiumlignosulfonate and sodium gluconate are preferred.

It is also preferred that the lignosulfonate compounds be refined.Without wishing to be bound by any theory, the refining process removescarbohydrates (mostly pentoses and hexoses). The use of lignosulfonatesbased on oxylignins is particularly preferred. Oxylignins are derivedfrom lignin that has been oxidized by the vanillin process.

The borate compound may be (but would not be limited to) boric acid,sodium metaborate, potassium metaborate, sodium diborate, potassiumdiborate, sodium triborate, potassium triborate, sodium tetraborate,potassium tetraborate, sodium pentaborate, potassium pentaborate andcombinations thereof. The borate compounds may contain waters ofhydration or be anhydrous. Sodium tetraborate decahydrate and sodiumpentaborate decahydrate are preferred.

Embodiments relate to methods for cementing a subterranean well,comprising providing a well-cementing composition that comprisesPortland cement, water and a retarder comprising a lignosulfonatecompound, a borate compound and a gluconate compound. The retarder isformulated such that the lignosulfonate:borate-compound concentrationratio is below about 0.75:1. The composition is placed in the well.Those skilled in the art will recognize that the method may pertain toboth primary and remedial cementing operations.

Embodiments relate to uses of a Portland-cement retarder comprising alignosulfonate compound, a borate compound and a gluconate compound,wherein the lignosulfonate:borate-compound concentration ratio is belowabout 0.75:1.

For all embodiments, the sodium lignosulfonate:sodium gluconateconcentration ratio is preferably between about 70:30 and 30:70.Moreover, the preferred ratio lignosulfonate:borate compounds:gluconatecompounds is between 0.1:1.0:0.1 and about 0.5:1.0:0.5, more preferablybetween 0.25:1.0:0.25 and 0.5:1.0:0.5. In yet even further preferredversion, when the borate compound comprises sodium tetraboratedecahydrate, the preferred sodium lignosulfonate:sodium tetraboratedecahydrate:sodium gluconate concentration ratio is preferably betweenabout 0.1:1.0:0.1 and about 0.5:1.0:0.5 by weight. Also, when the boratecompound comprises sodium pentaborate decahydrate, the preferred sodiumlignosulfonate:sodium pentaborate decahydrate:sodium gluconateconcentration ratio is preferably between about 0.1:1.0:0.1 and about0.5:1.0:0.5 by weight, and more preferably between about 0.25:1.0:0.25and about 0.5:1.0:0.5 by weight.

The cement compositions may further comprise more additives such as (butnot limited to) extenders, fluid-loss additives, lost-circulationadditives, additives for improving set-cement flexibility, self-healingadditives, antifoam agents, dispersants, gas generating additives andanti-settling agents.

EXAMPLES

The following examples serve to further illustrate the disclosure.

For all examples, cement slurries were prepared with Dyckerhoff BlackLabel Class G cement, at a density of 1917 kg/m³. Liquid additives wereadded to the mix fluid, and solid additives were dry blended with thecement.

The compounds that comprised the retarder formulations were sodiumlignosulfonate (an oxylignin), sodium gluconate and either sodiumtetraborate decahydrate or sodium pentaborate decahydrate.

All cement slurries contained 2.66 L/tonne of polypropylene-glycolantifoam agent. The test temperatures exceeded 110° C.; therefore,silica flour was added at a concentration of 35% by weight of cement(BWOC). An antisettling agent based on welan gum was often added todecrease the free-fluid volume.

The compatibility of the retarder formulations with a fluid-lossadditive (AMPS-acrylamide copolymer) and a gas-migration-preventionadditive (styrene-butadiene latex) was evaluated.

Cement-slurry preparation, free-fluid measurements, thickening-timemeasurements, fluid-loss measurements and rheological measurements wereperformed according to procedures published in ISO Publication 10426-2.Thickening-time tests were performed at three temperatures (Table 1).Fluid-loss measurements were performed with a stirred fluid-loss cell.

TABLE 1 Experimental Parameters for Thickening-Time Tests Time toInitial Final Initial Final Temperature/ Heating Temperature TemperaturePressure Pressure Pressure Rate (° C.) (° C.) (MPa) (MPa) (min) (°C./min) 27 110 12.1 92 29 2.86 27 150 13.8 111 34 3.62 27 176 13.8 15244 3.39

Example 1

Five cement slurries were prepared, all with the samesodium-tetraborate-decahydrate concentration: 2% BWOC. The combinedsodium-lignosulfonate and sodium-gluconate concentration was heldconstant at 1% BWOC. The sodium lignosulfonate-to-sodium gluconate ratiowas varied: 0:100; 25:75; 50:50, 75:25; and 100:0. The experimentalresults are given in Table 2.

TABLE 2 Effect of sodium lignosulfonate-to-sodium gluconate ratio oncement-slurry properties. Sodium Tetraborate (% BWOC) 2 2 2 2 2 SodiumLignosulfonate — 0.25 0.5 0.75 1 (% BWOC) Sodium Gluconate (% BWOC) 10.75 .5 0.25 — Mixing Rheology Plastic Viscosity (mPa · s) 132 142 129130 135 Yield Stress (Pa) 11.9 8.6 6.7 6.7 7.2 ISO/API Rheology at 85°C. Plastic Viscosity (mPa · s) 58 58 58 60 58 Yield Stress (Pa) 5.7 4.34.1 3.4 3.8 Free Fluid at 85° C. (%) 0.8 1.6 1.2 1.6 1.6 Thickening Timeat.176° C. 2:59 4:56 7:43 6:37 3:50 and 152 MPa (hr:min)

The thickening times were short when only either sodium gluconate orsodium lignosulfonate were present with sodium tetraborate decahydrate.However, when sodium gluconate and sodium lignosulfonate were presenttogether with sodium tetraborate decahydrate, the thickening times werelonger. This behavior highlights the synergy between sodiumlignosulfonate and sodium gluconate. As shown in FIG. 1, the longestthickening times are achieved when the sodium lignosulfonate-to-sodiumgluconate weight ratio is close to 50:50 (i.e., 0.5% BWOC sodiumlignosulfonate and 0.5% BWOC sodium gluconate).

The rheological properties and free-fluid values of the cement slurrieswere not significantly affected by varying the sodiumlignosulfonate-to-sodium gluconate ratio. The cement slurries were alsowell dispersed, as shown by the low yield-stress values.

Example 2

The concentrations of sodium lignosulfonate and sodium gluconate weremaintained constant at 0.5% BWOC. The concentration of sodiumtetraborate decahydrate was varied between 1% and 3% BWOC. Thethickening times of the cement slurries were measured at 176° C. and 152MPa. The experimental results are shown in Table 3.

TABLE 3 Effect of sodium-tetraborate-decahydrate concentration oncement-slurry properties. Sodium Tetraborate (% BWOC) 1 2 3 MixingRheology Plastic Viscosity (mPa · s) 156 129 153 Yield Stress (Pa) 106.7 11 ISO/API Rheology at 85° C. Plastic Viscosity (mPa · s) 61 58 63Yield Stress (Pa) 5.3 4.1 4.2 Free Fluid at 85° C. (%) 0.6 1.2 0.4Thickening Time at 176° C. 2:43 7:43 11:08 and 152 MPa (hr:min)

The thickening time was lengthened significantly when thesodium-tetraborate-decahydrate concentration increased. Maintaining aconstant sodium-lignosulfonate and sodium-gluconate concentrationhighlighted the strong synergy between the sodium tetraboratedecahydrate and the 50:50 mixture of sodium lignosulfonate and sodiumgluconate. The rheological properties and free-fluid values were notaffected significantly when the sodium-tetraborate-decahydrateconcentration was varied. The low yield-stress values show that theslurries were well dispersed.

Example 3

The sodium-tetraborate-decahydrate concentration needed to achieve longthickening times at 176° C. and 152 MPa was typically 1% to 3% BWOC. Thesolubility of sodium tetraborate decahydrate in water is about 50 g/L at25° C. This solubility is relatively low to formulate a practical liquidversion of the retarder.

The solubility of sodium pentaborate decahydrate in water is about 150g/L at 25° C.; therefore, it may be a better candidate to prepare aliquid retarder. Sodium pentaborate decahydrate contains 61.8 masspercent of B₁₀O₁₆, while sodium tetraborate decahydrate contains 40.8mass percent of B₄O₇. Thus, it would be expected that the pentaboratewould be the stronger retarder at an equal concentration. However, thechemical structures of the two borates being different, this may affecttheir performance. The performance of the two borates, in combinationwith a 50:50 blend of sodium lignosulfonate and sodium gluconate, wascompared at 176° C. and 152 MPa. The results are presented in Table 4.

TABLE 4 Performance of sodium pentaborate decahydrate vs sodiumtetraborate decahydrate. Sodium Tetraborate (% BWOC) 2 — — — SodiumPentaborate (% BWOC) — 1.42 2 2 Sodium Lignosulfonate (% BWOC) 0.5 0.50.5 0.75 Sodium Gluconate (% BWOC) 0.5 0.5 0.5 0.75 Mixing RheologyPlastic Viscosity (mPa · s) 129 150 160 162 Yield Stress (Pa) 6.7 6.29.1 7.2 ISO/API Rheology at 85° C. Plastic Viscosity (mPa · s) 58 61 6263 Yield Stress (Pa) 4.1 4.1 3.6 3.4 Free Fluid at 85° C. (%) 1.2 0.80.8 1.2 Thickening Time at 176° C. and 152 7:43 8:34 9:02 15:16 MPa(hr:min)

Keeping the sodium-lignosulfonate and sodium-gluconate concentrations at0.5% BWOC each, the sodium pentaborate retarder is slightly strongerthan the sodium tetraborate. A very long thickening time was obtainedwhen the sodium-lignosulfonate and sodium-gluconate concentrations wereraised to 0.75% BWOC, respectively. In the presence of sodiumpentaborate decahydrate, the plastic viscosity of the cement slurrieswas slightly higher than that of the slurry containing sodiumtetraborate decahydrate. All cement slurries were well dispersed, andthe free-fluid volumes were similar.

Example 4

A liquid retarder was prepared by dissolving 140 g of sodium pentaboratedecahydrate, 35 g of sodium lignosulfonate and 35 g of sodium gluconatein deionized water. Thus, the sodium pentaborate decahydrate-to-sodiumlignosulfonate+sodium gluconate ratio was 2 by weight.

The effect of the liquid retarder on the thickening time of cementslurries was tested at 176° C. and 152 MPa. Tests were performed withthe retarder alone, and in concert with either the AMPS-acrylamidefluid-loss additive or the styrene-butadiene latex. The liquid-retarderconcentration was 133 L/tonne of cement, corresponding to 1.67% BWOCsodium pentaborate decahydrate, 0.42% BWOC sodium lignosulfonate and0.42% BWOC sodium gluconate. Fluid-loss was also measured at 176° C. Theresults are presented in Table 5.

TABLE 5 Performance of a liquid retarder formulated with sodiumpentaborate, sodium lignosulfonate and sodium gluconate. Anti-SettlingAgent (% BWOC) 0.5 — 0.3 AMPS-Acrylamide Copolymer (L/tonne of cement) —58 — Styrene-Butadiene Latex (L/tonne of cement) — — 284 Liquid Retarder(L/tonne of cement) 133 133 133 Mixing Rheology Plastic Viscosity (mPa ·s) 125 306 158 Yield Stress (Pa) 7.2 8.1 12.9 ISO/API Rheology at 85° C.Plastic Viscosity (mPa · s) 60 125 90 Yield Stress (Pa) 4.0 4.3 5.3 FreeFluid at 85° C. (%) 1.5 2 2 Thickening Time at 176° C. and 152 MPa(hr:min) 8:11 13:51 11:13

The sodium pentaborate decahydrate formulation was a more efficientretarder than the sodium tetraborate decahydrate formulation (2.51% BWOCvs 3% BWOC as shown in Table 4). Again, AMPS-acrylamide copolymer andstyrene-butadiene latex acted as retarders. The rheological propertiesof the cement slurries and the free-water volumes were similar. Thefluid-loss volumes were slightly higher compared to those observed withsodium tetraborate decahydrate, but remained acceptable.

Example 5

The effect of the liquid retarder described in Example 4 was tested at110° C. and 92 MPa, and at 150° C. and 111 MPa. The liquid-retarderconcentration was 53 L/tonne of cement at 110° C. and 111 L/tonne ofcement at 150° C. The results are presented in Table 6.

TABLE 6 Performance of the inventive liquid retarder at 110° C. and 150°C.: Anti-Settling Agent (% BWOC) 0.1 0.4 Liquid Retarder (L/tonne ofcement) 53 89 Bottom Hole Circulating Temperature (° C.) 110 150 BottomHole Pressure 92 111 Thickening Time at BHCT and BHP (hr:min) 10:50 6:00

The results show that the retarder may be employed within a widetemperature range.

1. A well-cementing composition, comprising Portland cement, water and aretarder comprising a lignosulfonate compound, a borate compound and agluconate compound, wherein the lignosulfonate:borate-compoundconcentration ratio in the composition is lower than about 0.75:1, andthe lignosulfonate compound, the borate compound and the gluconatecompound are present in the blend at a lignosulfonate compound:boratecompound:gluconate compound concentration ratio between 0.1:1.0:0.1 and0.5:1.0:0.5 by weight, wherein the lignosulfonate compound is anoxylignin and the borate compound is sodium pentaborate decahydrate,sodium tetraborate decahydrate or both, and wherein the compositionfurther comprises AMPS-acrylamide copolymer or styrene butadiene latex.2. The composition of claim 1, wherein the lignosulfonate compoundcomprises sodium lignosulfonate, and the gluconate compound comprisessodium gluconate.
 3. The composition of claim 2, wherein the sodiumlignosulfonate:sodium gluconate concentration ratio is between about70:30 and about 30:70 by weight.
 4. (canceled)
 5. (canceled)
 6. Thecomposition of claim 1, wherein the retarder is liquid. 7-15. (canceled)